The invention relates to optics, and in particular the invention is concerned with optics for medical applications, as in optical detecting, diagnostic and therapeutic devices. The method and apparatus of the present invention are concerned with how a variety of multi-function optical components, all of which would normally be competing for the same reflected signals from a targeted object, can be made to operate simultaneously without significant degradation in performance from any of the component functions and without greatly increasing the required illumination levels. Examples of the variety of optical components considered are lasers, multiple real-time diagnostics, on-line video imaging, and other test and measurement equipment.
The history of lasers in medicine now spans nearly three decades. Initially, lasers constituted a new technology for medicine, and over the course of the decades an appreciation has developed for the variety of uses which a laser can serve as a therapeutic instrument. As confidence in the viability of lasers to perform therapeutic procedures has grown, new ways of using lasers are continually being studied in an effort to render them more efficacious for an ever increasing range of procedures.
In optical diagnostic equipment for medical purposes, particularly in ophthalmology and ophthalmic surgery, a number of different types of analysis and diagnosis, including topographical and shape imaging, cell counting, video microscope imaging and motion recognition, can be accomplished by directing rays of light reflected from target surfaces onto appropriate forms of detectors. As one example, see copending application Ser. No. 146,109 filed Dec. 22, 1989, now abandoned, and assigned to the same assignee as the present invention.
It may sometimes be desirable to perform a series of different diagnostic and therapeutic functions using co-axial illumination, a common beam of reflected light, such as in ophthalmic diagnosis or in support of ophthalmic surgery. Particularly in ophthalmic practice, it may sometimes be necessary or desirable to split a common reflected beam into a series of beams, such as for topographic imaging, for producing one or more video images, for detection of motion and other functions. In regard, see copending U. S. applications Ser. Nos. 307,315 and 456,109 filed Feb. 6, 1989 and Dec. 22, 1989, respectively, assigned to the same assignee as the present invention and incorporated by reference herein. The copending applications disclose imaging, tracking and corneal surface detecting equipment. Thus, increasing the effectiveness of laser procedures often requires the coaxial use of optical diagnostic imaging and sensing techniques to better identify the shape and location of individual targets. This can lead to competition for reflected light from the various diagnostic detectors desired. An example of this arises in ophthalmology whenever accurate refractive cataract or vitreo-retinal surgery calls for the on-line integration of a wide array of measurement devices, as indicated to some extent in the systems of the referenced patents.
In refractive surgery, the surgeon needs to know the initial shape of the cornea, the state of health of said cornea, and an indication of the shape of lesion which will lead to a desired ending shape for said cornea. Moreover, the surgeon needs to be able to establish where the laser lesion is to be positioned and to effect that lesion irrespective of patient eye motions. Furthermore, the surgeon needs to monitor the course of the procedure through some form of direct or indirect imaging.
The usual approach is to use white light illumination, at times polarized, at times subject to UV and IR filters, and essentially white light detectors for each and every different diagnostic element detector required. If only a small number of detectors are needed, this does not place an undue burden on available illumination levels. As more detectors are required, the standard approach is to increase the amount of illumination impingent on the eye to provide sufficient reflected radiance for detection. Another way often used in tandem is to use ever increasingly more sensitive detectors.
There are limitations to both the sensitivity of detectors and to the amount of illumination that a human eye can tolerate without eye damage, let alone discomfort. Also, lenses and reflectors and coatings on these optical elements have practical limits as to the intensity of light and heat that can be withstood without damage.
The spectrum of a typical white light source such as used for surgical illumination or ophthalmic diagnostic illumination purposes generally exhibits a Gaussian distribution. The intensity of the visible spectral portion of the white light is the greatest, with the mid-wavelengths at the peak of the curve. Intensity falls off sharply toward the infrared and ultraviolet ends of the spectrum.
It is known that optical coatings on the surfaces of lenses and mirrors can effect a spectral division of light impinging on the optical element. Such coatings have commonly been used on sunglasses and in various laser applications, causing selected portions of the spectrum, i.e. selected wavelength ranges of light, to be reflected and the remainder to be transmitted.
However, previous to the present invention spectral selectivity via optical coatings on beam splitters and similar optical elements has not been applied in the manner of the present invention described below, for enhancing the utility of a given light intensity for serving multiple diagnostic and imaging functions. In accordance with the invention relatively inexpensive detectors can be used in tandem working off of relatively similar levels of illumination.